Jan 3, 2012

Achieving Better Focus

by Amy Leavitt 

As a beginning photographer, I couldn't take a photo in focus to save my life. I tried many different apertures and f-stops. I set my shutter speed as high as I could. Still nothing. I read about how to hold the camera, and finally concluded that my camera's focus system was broken and needed to be repaired. I actually did a focus test (google it) to see if this was true. It wasn't. My focus system was fine. The problem was simply user error. Once I learned how my camera's focus system worked, I slowly but surely saw better results in my photos. So, please enjoy this simple and straight forward information on focus.
1. Know your camera's Focus System

Most DSLR's have 9 – 11 focus points. Some newer models have 50 or more. There are two types of focus points, single plane and cross point
Single plane will only work with lines of contrast that are perpendicular (at a 90 degree angle) to their orientation. So if you were shooting a skyscraper, a vertical object, a vertical focus point will not be able to find the edge of the building (the contrast) and it won't be able to focus. A horizontal focus point will be perpendicular to the building and would easily be able to find the contrast in order to focus.
Cross points contain both vertical and horizontal focus points, as shown by the square in the image below. Because a cross point has both vertical and horizontal sensors, they are the most accurate focus point. Some DSLR's only have one cross point in the center (like my Canon 5d), but newer, high-end cameras are now featuring cross points on all focus points.
Most cameras will look something like this:

The autofocus (AF) system in DSLR's works by adjusting the focus to achieve the best contrast between adjacent pixels on the focus sensor. 
If you are trying to photograph a subject that has little or no contrast, like a blue sky or even just a piece of white paper, the AF system cannot function because it can't find an "edge" or an area of contrast, and your camera will not focus.
To better understand how the focus points work, choose a vertical focus point and try to focus on the following image. Because the focus sensor can't find an edge, it will not focus.
The focus points are looking for contrasting pixels perpendicular to their orientation, not parallel. To illustrate this, go to the above image again. Try to focus on the black line using a horizontal focus point. It will easily find the edge and focus.

2. Use the Correct Focus Mode

Avoid using the "all focus point" mode, where the camera chooses the area of focus. There are sometimes when this is handy, like in fast situations or when you just need to get the shot. But for portrait, wedding or commercial work, you'll likely want total control on the area of focus.

One-Shot or Single Servo (for still subjects) – When you press the shutter button halfway down, the camera locks on your focus point. You can recompose the shot and press the shutter all the way down to take the photo. The focus stays locked until you press the shutter or re-press the shutter to lock on a new point.

AI Servo or Continuous Servo (for moving subjects) – When you press the shutter button halfway down, the camera will focus on the subject continually and refocus if the camera or the subject moves. It will attempt to track your subject and predict the correct focus area when the shutter is pressed. This is useful for sports, action or fast moving subjects, like toddlers, or a child on a swing.

Manual Focus - You adjust the focus manually by turning the focus ring on your lens. I rarely use this mode, but it can be useful in macro photography or low light situations. I've also used this when I purposely want to blur a subject, as in the example below:

3.  The Focus and Recompose Method

This can sometimes be a subject of debate in the photography world. So let me qualify this by saying that if it works for you, do it. If it doesn't, don't. 

The focus and recompose method is exactly what it's name says: Focus on what you want sharp in the image, i.e. the eye of the subject, press the shutter halfway to lock focus, then recompose or frame the image according to your artistic taste. I use this 90% of the time when I'm shooting portraits because I only have one cross point in the center of the frame. I don't always want my subject in the center, however. So I will center the middle cross point over my subject's eye, then recompose so that they are not dead center.

The reason why this may be a hot topic is because of the fact that when you recompose, you are moving the focal plane and thus your shot might turn out soft. This can be true, if you're using wide open apertures, where moving the focal plane can make a big difference. However, I consciously use this method when I know a slight adjustment in the focal plane won't lose sharpness on my subject. I don't use this method if I'm up close and/or using a wide open aperture.

4. Focus on What's Important
What should you focus on in the image? For portraits, you should focus on the eyes. Focus on the part of the image that you want to draw the viewers attention to. For groups, choose a subject near the middle and focus on their eye (use a small aperture). For landscapes, where you want everything in focus, choose the smallest aperture and focus on a subject in the foreground and let the depth of field carry the area of focus to the background.

5. Don't Use Photoshop to Try to Fix Focus Errors
If an image is out of focus, sharpening it in Photoshop won't ultimately make it in focus. You'll just have a sharp image that's still out of focus. Unsharp Mask, Smart Sharpen or High-Pass filtering are there to sharpen in-focus photos, not to fix out of focus photos. 

6. Common Reasons for Blurry Photos
Blurry photos can occur for a variety of reasons:
  • Camera shake: Every person has a different "safe" shutter speed. Find out the lowest shutter speed where you can handhold the camera without camera shake. You may have steady hands and can hold the camera as low as 1/60 without camera shake. My limit is 1/125.
  • Slow shutter speed: If your subject is moving, it won't matter how steady your hands are. Use a faster shutter speed if you don't want action blur.
  • Improper focusing of the focus points: If you're trying to use the wrong type of focus point, the camera will either not be able to focus, or it will choose the closest area of contrast to focus on, which may not be where you want.
  • Improper Exposure: If you have bad lighting or your image is underexposed, it will look out of focus, no matter how hard you try. Be sure your subject is well lit and your exposure is spot on.

1 comment:

Anonymous said...

I have to correct on where to focus when shooting landscapes. One should use a method called hyperfocal focusing. If one were to focus on the foreground even using F16 then the background would be slightly out of focus and one wouldn't maximize the sharpness or depth of field. One shouldn't go higher than F16 because the image quality will suffer because of defraction. Here are a couple links on how to use hyperfocal focusing.